There are various fields of application for communication or transmission systems in which data of a certain data type are transmitted cyclically.
For example, there are fields of application in which the existence of a data transmission link of the communication or transmission system is continuously checked by cyclically transmitting data of a particular data type.
As a supplement or as an alternative, data of a data type to be transmitted cyclically in the fields of process control usually in each case comprise process-related process data which must be updated at regular intervals and provided for the participant units involved in the process via corresponding communication or transmission systems in order to control a particular process in accordance with the requirements.
Such process data are, for example, IN process data or process input data, cyclically detected by means of sensors such as, for example, sensors at a slave participant unit within a master-slave system, which are transmitted to a master participant unit for further processing, and OUT-process data or process output data, calculated by a master participant unit which, in turn, are transmitted to participant units communicating with actuators such as for example actuating elements and/or drives for correspondingly driving the actuators. As soon as such process data are relevant to a process to be controlled, they must be transmitted cyclically, in consequence. A particular relevance of such process data is found in applications in fields of safety engineering in which application-specific safety-related process input and/or process output data must be detected regularly via safety-related participant units and output via safety-related participant units, respectively, in order to be able to detect safety-critical errors during a process sequence which could also represent a hazard for human beings as early as possible and, if necessary, move an erroneous process or part-process into a safe state within short response times.
Data of a data type which can be transmitted acyclically are, for example, diagnostic data or acknowledgment data which are only transmitted when required or on request. When such data are transmitted, however, the times of the transmission of data of a data type to be transmitted cyclically such as, e.g. of process data, are usually changed and thus inadmissibly disturbed for many applications. Such a change of the times of the transmission of data of a data type to be transmitted cyclically is inadmissible, for example, in applications which require an equidistant transmission in time as is the case, in particular, in safety engineering. Furthermore, the worst-case response times of the transmission system are also usually extended by the transmission of data of an acyclic data type such as, for example, diagnostic data or also acknowledgement data, which is also of great relevance particularly in the fields of safety engineering. In addition, there is scarcely any more deterministic in the transmission of data via the transmission channel particularly if the same transmission path or channel is used for the transmission of data of a data type which can be transmitted acyclically as for the transmission of data of a data type to be transmitted cyclically.